Hollow metal article and method of producing the same



June 21,1927 1,633,187 I A; B. NORTON HOLLOW METAL ARTICLE AND METHOD OF PRODUCING THE SAME" Filed Jan. 15. 1926 INVENTOR I ATTzfiN EY Patented June 21, i927.

UNITED s A -ps "1,633,187 PATENT OFFICE.

ALLEN BPNORTON, OF CLEVELAND, OHIO, ASSIO-NOR TO ALUMINUM COMPANY OF AMERICA, PITTSBURGH, PENNSYLVANIA, A CORPORATION O PENNSYLVANIA.

HOLLOW METAL ARTICLE AND METHOD OF PRODUCING THE SAME.

Application filed January 13, 1926. Serial no. 80,902.

This invention relates to the art of manufacturing hollow metal articles and is.con-

cerned more especially with the construction of pistons for internal combustion enmes. g One object of the invention is to devise a method of constructing hollow metal articles which, when split longitudinally, will auto matically change in diametrical dimensions.

Another object is to construct an internal combustion engine piston by simple mechanical means which when split lengthwise of the skirt will automatically increase in diametrical dimensions in the split portion thereof. I

In the drawings attached to and forming a part off'this specification:

Fig. 1 is a perspective View of a hollow metal article upon which my method may be practiced;

Figs. 2 and 3 are, respectively, transverse sections of an article similar to that shown in Fig. 1 but representing the change in diametrical dimensions induced by my method.

Fig. 4 is a longitudinal sectional view of a pistonfor an internal combustion engine which has been constructed in accordance with my invention; and a Fig. 5 is a transverse sectional view taken on line 5-5 of Fig. 4.

I have discovered that hollow metal articles can be so treated as to expand or contract or, in other words, to change in diametrical dimension upon being split longitudinally. The preferred method of accomplishing this result is by producing stress inthe surface layers of t e article and then splitting the article longitudinally or in a generally lengthwise direction. The stress induced should be greater in one surface layer than in the oppo'slte surface layer to produce noticeable results and in general the greater the difference in stresses the eater the change in diameter after splittmg of the article. Stresses may be induced in such surface layers by various means, but I prefer to accomplish this by sim le mechanical means and operations whic conveniently may consist of burnishing or rolling or otherwise compressing the surface la. er of a hollow article in amanner to leave in a state of compression.

In Fig. 2, I have illustrated a section of a hollow cylinder or tube, the dotted lines-int e layer dicating the position of the parts of the article before being split longitudinally as at 2. Before splitting, the article was subjected to a burnishing or rolling operation which left the inner surface in a state of compression. Reference character 3 indicates generally the extent and location of the compressed layer of metal. After the article 1 was thus compressed it was split longitudinally as at 2, whereupon it increased its diametrical dimensions by reason of the outward movement of the walls as indicated substantially by the full lines in this figure. I

In Fig. 3, a similar article 1 was burnished or rolled or similarly acted upon to produce a layer of metal 3 at and adjacent to the outer surface thereof, which was left in a state of compression. Upon being split longitudinally as at-4, the article contracted into the full line position in the figure.

The change in shapeand dimensions of a hollow metal article treated by my method is slightly different when intersecting slits, such as 5 and 6, (Figs. 4 and 5) are formed in the hollow article, since the transverse slot 5 permits the tongue-like portions of the article along split 6 to spring outwardly or inwardly as the case may be substantially parallel to the remaining parts of the article.

When only a longitudinal s lit is formed, the tendency is, of course, or the greater change in diameter to occur at the open end of the article and the least expansion or contraction to be present at the closed end of the longitudinal split. In the caseof a piston of the type shown where the heavy bosses are a part of or connected directly to the skirt, the greatest expansion is at the open end, even when a transverse'or eircumferential slot is used, since the boss section is of greater stiffness o'r rigidity than the walls at the open end of the skirt.

In piston 7 of Figs. 4 and 5, the piston after being cast and machined and before formation of the slits 5 and 6 in the skirt thereof is subjected to'a compression producing operation on its inner surface from the open end of the skirt up to or toward the bosses 8. I Preferably, this compressing operation is carried out by a burnishing operation, while the piston is still mounted in the lathe where it was machined, although obviously a subsequent operation may be employed if desired. After the inner surface ayer of the skirt has been so compressed as at 9, the skirt is split longitudinally. It is preferable to extend the longitudinal split 6 to intersect the transverse split 5,.but this which comprises forming the metal pistons,

transverse split may in certain cases be omitted if desired. The full lines in Fig. indicate the nature of the change of the skirt after being so compressed and split, the dotted lines indicating the skirt before compression and splitting.

Although articles constructed in accordance with my invention may be of general use, I have found the invention to be of considerable value in connection with aluminum skilled in the art may practice the same, and

alloy pistons for internal combustion engines which are to be split lengthwise, since the piston tends to become larger in diameter across the bearing faces and also to resist side thrust of the piston which would tend to bend the tongue-like portions of the skirt inwardly and give them a permanent set within their normal circumference. Pistons constructed in accordance with my invention appear to be more resistant to inward movement by these side thrusts and to retain their normal shape much longer 'in use than pistons formed by merely splitting the ordinary piston casting.

'Although I have described my invention in detail with reference to two different structures, I have done so merelyfor the purpose of disclosing my invention so that those not for the purpose of limiting my invention thereto. The Scope of my invention is defined inwhat is claimed.

What is claimed is: 1. A piston having a skirt split longitudinally and having mechanically induced compression stresses in the metal adjacent the inner surface of the lower part'of the skirt. 2.. The method of constructing pistons mechanically impressing compression stresses in the metal adjacent one surface oft-he skirt thereof, and then splitting the skirt longitudinally.

3. The method of constructing a piston which comprises forming the piston, me; chanically compressing the metal. at the inner surface of the skirt thereof, and then splitting the skirt longitudinally.

4. The method of constructing a piston which comprises forming. the piston, me-

chanically compressing the inner surface layers of the skirt thereof so as to leave said surface layers in a state of compression, and then forming intersecting splits in the skirt, one of which extends through the compressed portion of the piston.

5. A piston having a hollow skirt splitlongitudinally, the inner surface of the lower part of the skirt being mechanically compressed.

6. A piston comprising a head, wrist pin bosses depending therefrom, and a skirt, the metal adjacent the inner surface of the skirt being mechanically compressed below said bosses.

7. A piston comprising a head, delplending wrist-pin bosses therebelow, and a s 'rt, the

skirt being mechanically compressed at its 

